The invention relates to thermoreactive hot-melt adhesives based on polyurethane.
Polyurethane adhesives (PUR-hot-melt adhesives) of prepolymers based on polyadipic acid derivatives or polyglycol derivatives and polyisocyanates are known, for example, from EP-B-455 400. These PUR-hot-melt adhesives are used for the bonding of synthetic materials, glass, metal, leather or wood and cure irreversibly, due to the effect of the humidity in the air or in the materials being adhered.
EP-A 0 431 413 describes a thermally curable PUR-powder based on polyurethane with encapsulated isocyanates, whereby the de-activation of the isocyanate groups is not brought about by capping, but by a blocking layer on the surface of the particle. Particulate materials are used as components in the formulation. In order to generate powder-shaped products, it is necessary to add the reaction mixture as a melt to an inert solvent/emulsifier system.
EP-A 419 928, DE-A 199 63 585 and EP-A 1 217 018 describe thermally curable PUR-adhesives comprising isocyanate group containing polymers in mixture with polyalkohols and polyamines. The incomplete heat stability of the cured adhesives for the use in the field of technical constructions is a disadvantage of these adhesives.